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<H1>Milter API</H1>

<H2>Contents</H2>
<UL>
    <LI><A HREF="#LibraryControlFunctions">Library Control Functions</A>
    <LI><A HREF="#DataAccessFunctions">Data Access Functions</A>
    <LI><A HREF="#MessageModificationFunctions">Message Modification Functions</A>
    <LI><A HREF="#Callbacks">Callbacks</A>
    <LI><A HREF="#Miscellaneous">Miscellaneous</A>
</UL>

<H2><A NAME="LibraryControlFunctions">Library Control Functions</A></H2>

Before handing control to libmilter (by calling
<A HREF="smfi_main.html">smfi_main</A>), a filter may call the following
functions to set libmilter parameters.
In particular, the filter must call
<A HREF="smfi_register.html">smfi_register</A> to register its callbacks.
Each function will return either MI_SUCCESS or MI_FAILURE to
indicate the status of the operation.

<P>
None of these functions communicate with the MTA.
All alter the library's state, some of which
is communicated to the MTA inside
<A HREF="smfi_main.html">smfi_main</A>.

<P>
<TABLE BORDER="1" CELLSPACING=0 CELLPADDING=2><TR BGCOLOR="#dddddd"><TH>Function</TH><TH>Description</TH></TR>

<TR><TD><A HREF="smfi_opensocket.html">smfi_opensocket</A></TD><TD>Try to create the interface socket.</TD></TR>

<TR><TD><A HREF="smfi_register.html">smfi_register</A></TD><TD>Register a filter.</TD></TR>

<TR><TD><A HREF="smfi_setconn.html">smfi_setconn</A></TD><TD>Specify socket to use.</TD></TR>

<TR><TD><A HREF="smfi_settimeout.html">smfi_settimeout</A></TD><TD>Set timeout.</TD></TR>

<TR><TD><A HREF="smfi_setbacklog.html">smfi_setbacklog</A></TD><TD>Define the incoming <CODE>listen(2)</CODE> queue size.</TD></TR>

<TR><TD><A HREF="smfi_setdbg.html">smfi_setdbg</A></TD><TD>Set the milter library debugging (tracing) level.</TD></TR>

<TR><TD><A HREF="smfi_stop.html">smfi_stop</A></TD><TD>Cause an orderly shutdown.</TD></TR>

<TR><TD><A HREF="smfi_main.html">smfi_main</A></TD><TD>Hand control to libmilter.</TD></TR>

</TABLE>

<H2><A NAME="DataAccessFunctions">Data Access Functions</A></H2>

The following functions may be called from within the filter-defined callbacks
to access information about the current connection or message.
<P>
<TABLE BORDER="1" CELLSPACING=0 CELLPADDING=2><TR bgcolor="#dddddd"><TH>Function</TH><TH>Description</TH></TR>
<TR><TD><A HREF="smfi_getsymval.html">smfi_getsymval</A></TD><TD>Return the value
of a symbol.</TD></TR>

<TR><TD><A HREF="smfi_getpriv.html">smfi_getpriv</A></TD><TD>Get the private data
pointer.</TD></TR>

<TR><TD><A HREF="smfi_setpriv.html">smfi_setpriv</A></TD><TD>Set the private data
pointer.</TD></TR>

<TR><TD><A HREF="smfi_setreply.html">smfi_setreply</A></TD><TD>Set the specific
reply code to be used.</TD></TR>

<TR><TD><A HREF="smfi_setmlreply.html">smfi_setmlreply</A></TD><TD>Set the
specific multi-line reply to be used.</TD></TR>

</TABLE>

<H2><A NAME="MessageModificationFunctions">Message Modification Functions</A></H2>

The following functions change a message's contents and attributes.
<EM>They may only be called in <A HREF="xxfi_eom.html">xxfi_eom</A></EM>.
All of these functions may invoke additional communication with the MTA.
They will return either MI_SUCCESS or MI_FAILURE to indicate the status of
the operation.
Message data (senders, recipients, headers, body chunks)
passed to these functions via parameters is copied and does not need to be
preserved (i.e., allocated memory can be freed).

<P>
A filter which might call a message modification function
must set the appropriate flag
(<A HREF="#SMFIF">listed below</A>),
either
in the description passed to <A HREF="smfi_register.html">smfi_register</A>
or via <A HREF="xxfi_negotiate.html">xxfi_negotiate</A>.
Failure to do so will cause the MTA to treat a call to the function
as a failure of the filter, terminating its connection.

<P>
Note that the status returned indicates only whether or not the
filter's message was successfully sent to the MTA, not whether or not
the MTA performed the requested operation.
For example,
<A HREF="smfi_addheader.html">smfi_addheader</A>, when called with an
illegal header name, will return MI_SUCCESS even though the MTA may
later refuse to add the illegal header.
<P>
<TABLE BORDER="1" CELLSPACING=0 CELLPADDING=2><TR BGCOLOR="#dddddd"><TH>Function</TH><TH>Description</TH><TH><A NAME="SMFIF">SMFIF_* flag</A></TH></TR>
<TR><TD><A HREF="smfi_addheader.html">smfi_addheader</A></TD><TD>Add a header to
the message.</TD><TD>SMFIF_ADDHDRS</TD></TR>

<TR><TD><A HREF="smfi_chgheader.html">smfi_chgheader</A></TD><TD>Change or delete a header.</TD><TD>SMFIF_CHGHDRS</TD></TR>

<TR><TD><A HREF="smfi_insheader.html">smfi_insheader</A></TD><TD>Insert a
header into the message.</TD><TD>SMFIF_ADDHDRS</TD></TR>

<TR><TD><A HREF="smfi_chgfrom.html">smfi_chgfrom</A></TD><TD>Change the
envelope sender address.</TD><TD>SMFIF_CHGFROM</TD></TR>

<TR><TD><A HREF="smfi_addrcpt.html">smfi_addrcpt</A></TD><TD>Add a recipient to
the envelope.</TD><TD>SMFIF_ADDRCPT</TD></TR>

<TR><TD><A HREF="smfi_addrcpt_par.html">smfi_addrcpt_par</A></TD><TD>Add
a recipient including ESMTP parameter to the envelope.
</TD><TD>SMFIF_ADDRCPT_PAR</TD></TR>

<TR><TD><A HREF="smfi_delrcpt.html">smfi_delrcpt</A></TD><TD>Delete a recipient
from the envelope.</TD><TD>SMFIF_DELRCPT</TD></TR>

<TR><TD><A HREF="smfi_replacebody.html">smfi_replacebody</A></TD><TD>Replace the
body of the message.</TD><TD>SMFIF_CHGBODY</TD></TR>

</TABLE>

<H2>Other Message Handling Functions</H2>

The following functions provide special case handling instructions for
milter or the MTA, without altering the content or status of the message.
<EM>They too may only be called in <A HREF="xxfi_eom.html">xxfi_eom</A></EM>.
All of these functions may invoke additional communication with the MTA.
They will return either MI_SUCCESS or MI_FAILURE to indicate the status of
the operation.

<P>
Note that the status returned indicates only whether or not the
filter's message was successfully sent to the MTA, not whether or not
the MTA performed the requested operation.

<P>
<TABLE BORDER="1" CELLSPACING=0 CELLPADDING=2><TR BGCOLOR="#dddddd"><TH>Function</TH><TH>Description</TH></TR>
<TR><TD><A HREF="smfi_progress.html">smfi_progress</A></TD><TD>Report operation in progress.</TD></TR>

<TR><TD><A HREF="smfi_quarantine.html">smfi_quarantine</A></TD><TD>Quarantine a message.</TD></TR>

</TABLE>

<H2><A NAME="Callbacks">Callbacks</A></H2>

The filter should implement one or more of the following callbacks,
which are registered via <A HREF="smfi_register.html">smfi_register</A>:

<P>
<TABLE BORDER="1" CELLSPACING=0 CELLPADDING=2><TR BGCOLOR="#dddddd"><TH>Function</TH><TH>Description</TH></TR>

<TR><TD><A HREF="xxfi_connect.html">xxfi_connect</A></TD><TD>connection info</TD></TR>

<TR><TD><A HREF="xxfi_helo.html">xxfi_helo</A></TD><TD>SMTP HELO/EHLO command</TD></TR>

<TR><TD><A HREF="xxfi_envfrom.html">xxfi_envfrom</A></TD><TD>envelope sender</TD></TR>

<TR><TD><A HREF="xxfi_envrcpt.html">xxfi_envrcpt</A></TD><TD>envelope recipient</TD></TR>

<TR><TD><A HREF="xxfi_data.html">xxfi_data</A></TD><TD>DATA command</TD></TR>

<TR><TD><A HREF="xxfi_unknown.html">xxfi_unknown</A></TD><TD>Unknown SMTP command</TD></TR>

<TR><TD><A HREF="xxfi_header.html">xxfi_header</A></TD><TD>header</TD></TR>

<TR><TD><A HREF="xxfi_eoh.html">xxfi_eoh</A></TD><TD>end of header</TD></TR>

<TR><TD><A HREF="xxfi_body.html">xxfi_body</A></TD><TD>body block</TD></TR>

<TR><TD><A HREF="xxfi_eom.html">xxfi_eom</A></TD><TD>end of message</TD></TR>

<TR><TD><A HREF="xxfi_abort.html">xxfi_abort</A></TD><TD>message aborted</TD></TR>

<TR><TD><A HREF="xxfi_close.html">xxfi_close</A></TD><TD>connection cleanup</TD></TR>

<TR><TD><A HREF="xxfi_negotiate.html">xxfi_negotiate</A></TD><TD>option negotiation</TD></TR>

</TABLE>

<P>
The above callbacks should all return one of the following return values,
having the indicated meanings.
Any return other than one of the below values constitutes an error,
and will cause sendmail to terminate its connection to the offending filter.

<P><A NAME="conn-spec">Milter</A> distinguishes between recipient-,
message-, and connection-oriented routines.
Recipient-oriented callbacks may affect the processing
of a single message recipient;
message-oriented callbacks, a single message;
connection-oriented callbacks, an entire connection
(during which multiple messages may be delivered
to multiple sets of recipients).
<A HREF="xxfi_envrcpt.html">xxfi_envrcpt</A> is recipient-oriented.
<A HREF="xxfi_negotiate.html">xxfi_negotiate</A>,
<A HREF="xxfi_connect.html">xxfi_connect</A>,
<A HREF="xxfi_helo.html">xxfi_helo</A> and
<A HREF="xxfi_close.html">xxfi_close</A> are connection-oriented.
All other callbacks are message-oriented.

<P>
<TABLE BORDER="1" CELLSPACING=0 CELLPADDING=2>
  <TR BGCOLOR="#dddddd"><TH>Return value</TH><TH>Description</TH></TR>
  <TR VALIGN="TOP">
     <TD>SMFIS_CONTINUE</TD>
     <TD>Continue processing the current connection, message, or recipient.
     </TD>
  </TR>
  <TR VALIGN="TOP">
     <TD>SMFIS_REJECT</TD>
     <TD>For a connection-oriented routine, reject this connection; call <A HREF="xxfi_close.html">xxfi_close</A>.<BR>
        For a message-oriented routine (except
        <A HREF="xxfi_abort.html">xxfi_abort</A>), reject this message.<BR>
	For a recipient-oriented routine, reject the current recipient (but continue processing the current message).
     </TD>
  </TR>
  <TR valign="top">
     <TD>SMFIS_DISCARD</TD>
     <TD>For a message- or recipient-oriented routine, accept this message, but silently discard it.<BR>
     SMFIS_DISCARD should not be returned by a connection-oriented routine.
     </TD>
  </TR>
  <TR valign="top">
     <TD>SMFIS_ACCEPT</TD>
     <TD>For a connection-oriented routine, accept this connection without further filter processing; call <A HREF="xxfi_close.html">xxfi_close</A>.<BR>
         For a message- or recipient-oriented routine, accept this message without further filtering.<BR>
     </TD>
  </TR>
  <TR valign="top">
     <TD>SMFIS_TEMPFAIL</TD>
     <TD>Return a temporary failure, i.e., the corresponding SMTP command will return an appropriate 4xx status code.
	 For a message-oriented routine (except <A HREF="xxfi_envfrom.html">xxfi_envfrom</A>), fail for this message.<BR>
	 For a connection-oriented routine, fail for this connection; call <A HREF="xxfi_close.html">xxfi_close</A>.<BR>
	 For a recipient-oriented routine, only fail for the current recipient; continue message processing.
     </TD>
  </TR>

  <TR valign="top">
     <TD><A NAME="SMFIS_SKIP">SMFIS_SKIP</A></TD>
     <TD>Skip further callbacks of the same type in this transaction.
	Currently this return value is only allowed in
	<A HREF="xxfi_body.html">xxfi_body()</A>.
	It can be used if a milter has received sufficiently many
	body chunks to make a decision, but still wants to invoke
 	message modification functions that are only allowed to be called from
	<A HREF="xxfi_eom.html">xxfi_eom()</A>.
	Note: the milter <EM>must</EM>
	<A HREF="xxfi_negotiate.html">negotiate</A>
	this behavior with the MTA, i.e., it must check whether
	the protocol action
	<A HREF="xxfi_negotiate.html#SMFIP_SKIP"><CODE>SMFIP_SKIP</CODE></A>
	is available and if so, the milter must request it.
     </TD>
  </TR>

  <TR valign="top">
     <TD><A NAME="SMFIS_NOREPLY">SMFIS_NOREPLY</A></TD>
     <TD>Do not send a reply back to the MTA.
	The milter <EM>must</EM>
	<A HREF="xxfi_negotiate.html">negotiate</A>
	this behavior with the MTA, i.e., it must check whether
	the appropriate protocol action
	<A HREF="xxfi_negotiate.html#SMFIP_NR_"><CODE>SMFIP_NR_*</CODE></A>
	is available and if so, the milter must request it.
	If you set the
	<A HREF="xxfi_negotiate.html#SMFIP_NR_"><CODE>SMFIP_NR_*</CODE></A>
	protocol action for a callback, that callback <EM>must</EM>
	always reply with
	SMFIS_NOREPLY.
	Using any other reply code is a violation of the API.
	If in some cases your callback may return another value
	(e.g., due to some resource shortages), then you
	<EM>must not</EM> set
	<A HREF="xxfi_negotiate.html#SMFIP_NR_"><CODE>SMFIP_NR_*</CODE></A>
	and you must use
	SMFIS_CONTINUE as the default return code.
	(Alternatively you can try to delay reporting the problem to
	a later callback for which
	<A HREF="xxfi_negotiate.html#SMFIP_NR_"><CODE>SMFIP_NR_*</CODE></A>
	is not set.)
     </TD>
  </TR>

</TABLE>

<H2><A NAME="Miscellaneous">Miscellaneous</A></H2>

<P>
<TABLE BORDER="1" CELLSPACING=0 CELLPADDING=2><TR BGCOLOR="#dddddd"><TH>Function</TH><TH>Description</TH></TR>

<TR><TD><A HREF="smfi_version.html">smfi_version</A></TD><TD>libmilter (runtime) version info</TD></TR>

<TR><TD><A HREF="smfi_setsymlist.html">smfi_setsymlist</A></TD><TD>
Set the list of macros that the milter wants to receive from the MTA
for a protocol stage.
</TD></TR>

</TABLE>

<P>
<TABLE BORDER="1" CELLSPACING=0 CELLPADDING=2><TR BGCOLOR="#dddddd"><TH>Constant</TH><TH>Description</TH></TR>

<TR><TD><A HREF="smfi_version.html">SMFI_VERSION</A></TD><TD>libmilter (compile time) version info</TD></TR>

</TABLE>


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